| Message ID | 153616290368.23468.7806230605345568524.stgit@warthog.procyon.org.uk (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | [01/11] UAPI: drm: Fix use of C++ keywords as structural members | expand |
On Wed, 05 Sep 2018 16:55:03 +0100, David Howells wrote: > >The bkey struct defined by bcache is embedded in the jset struct. However, >this is illegal in C++ as there's a "flexible array" at the end of the struct. >Change this to be a 0-length struct instead. > >- __u64 ptr[]; >+ __u64 ptr[0]; As per the C++ standard, it is _also_ illegal to declare an array of size zero. """it [the array size expression] shall be a converted constant expression of type std::size_t and its value shall be greater than zero.""" —http://eel.is/c++draft/dcl.array That makes both "__u64 ptr[]" and "__u64 ptr[0]" *implementation-specific extensions*. 3rd party tooling (concerns both C and C++): Coverity Scan (IIRC) treats "__u64 ptr[0]" as an array of "definitely-zero" size. Writing to any element will outright flag an out-of-bounds violation. That is sensible, since only "ptr[]" was standardized. Conclusion: So please, do never use __u64 ptr[0].
Jan Engelhardt <jengelh@inai.de> wrote: > """it [the array size expression] shall be a converted constant expression of > type std::size_t and its value shall be greater than zero.""" > —http://eel.is/c++draft/dcl.array Interesting. You're not actually quoting the full sentence: If the constant-expression is present, it shall be a converted constant expression of type std::size_t and its value shall be greater than zero. This suggests that: __u64 ptr[] is actually valid since: D1 [ constant-expressionopt ] attribute-specifier-seqopt suggests that the part between the brackets is optional. David
On Tuesday 2018-10-09 17:41, David Howells wrote: >Jan Engelhardt <jengelh@inai.de> wrote: > >> """it [the array size expression] shall be a converted constant expression of >> type std::size_t and its value shall be greater than zero.""" >> —http://eel.is/c++draft/dcl.array > >Interesting. You're not actually quoting the full sentence: > > If the constant-expression is present, it shall be a converted > constant expression of type std::size_t and its value shall be > greater than zero. > >This suggests that: > > __u64 ptr[] > >is actually valid I think that kind of validity only goes for this kind of standalone decl: extern int myints[]; but not for []-inside-struct.
diff --git a/include/uapi/linux/bcache.h b/include/uapi/linux/bcache.h index 5d4f58e059fd..11863e903bff 100644 --- a/include/uapi/linux/bcache.h +++ b/include/uapi/linux/bcache.h @@ -23,7 +23,7 @@ static inline void SET_##name(type *k, __u64 v) \ struct bkey { __u64 high; __u64 low; - __u64 ptr[]; + __u64 ptr[0]; }; #define KEY_FIELD(name, field, offset, size) \
The bkey struct defined by bcache is embedded in the jset struct. However, this is illegal in C++ as there's a "flexible array" at the end of the struct. Change this to be a 0-length struct instead. Signed-off-by: David Howells <dhowells@redhat.com> cc: Coly Li <colyli@suse.de> cc: Kent Overstreet <kent.overstreet@gmail.com> cc: linux-bcache@vger.kernel.org --- include/uapi/linux/bcache.h | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)